Dietary factors play an important role in the etiology of different kinds of cancer (Greenwald et al., 2001). For example, soybean-rich diets are associated with lower cancer mortality rates, particularly for cancers of the colon, breast and prostate (Messina et al., 1994). Isoflavones and the Bowman-Birk protease inhibitor (BBI) are some of the many components in soybean believed to be responsible for suppressing carcinogenesis (Kennedy, 1995). Recently, lunasin, a small peptide found in soybean seeds, has shown promise as a agent that reduces the neoplastic effects of certain carcinogenic chemicals (a “anti-neoplastic” agent) (Galvez et al., 2001).
Lunasin is a 43 amino acid small subunit of a soybean 2S albumin. The polynucleotide encoding the lunasin peptide, and the peptide sequence of lunasin are known and disclosed in U.S. Pat. No. 6,544,956 (hereby incorporated by reference in its entirety) in which the lunasin peptide is encoded by bases 80-208 of SEQ ID NO:1, and the peptide is defined by residues 22-64 of SEQ ID NO:2. The carboxyl end of lunasin contains a chromatin-binding domain, a cell adhesion motif Arg-Gly-Asp (RGD) followed by eight Asp residues (Galvez and de Lumen, 1997; Galvez and de Lumen, 1999). The chromatin-binding domain consists of a 10-amino acid helical region homologous to a short conserved region found in other chromatin binding proteins (Aasland and Stewart, 1995). Mammalian studies provide evidence that lunasin may play a role in the cell cycle control (Galvez and de Lumen, 1999; Galvez et al., 2001; Jeong et al., 2002). For example, transfection of the lunasin gene into mammalian cells results in mitotic arrest and subsequent cell death (Galvez and de Lumen, 1999). In addition, exogenous addition of chemically synthesized lunasin to mammalian cells demonstrates that lunasin colocalizes with hypoacetylated chromatin; preferentially binds deacetylated histone H4 in vitro; and prevents histone H3 and H4 acetylation in vivo in the presence of a histone deacetylase inhibitor (Galvez et al., 2001). Acetylation and deacetylation of conserved histone N-terminal tails result in chromatin conformational changes that induce or suppress gene expression. It has been hypothesized that Lunasin modulates changes in chromatin organization by modifying histone tails, thereby, affecting gene expression that leads to its anti-neoplastic properties. Recently, lunasin was isolated from barley and was reported to possess the same biological activity ascribed to chemically synthesized lunasin (Jeong et al., 2002).
While transfection of a cell with lunasin leads to cell death, lunasin peptide has been shown to have anti-neoplastic properties (Galvez et al., 2001). Significant suppression of chemical carcinogen-induced, e.g. 7,12-dimethylbenz[a]-anthracene (DMBA) and 3-methylcholanthrene (MCA), foci formation in C3H 10T1/2 mouse embryo fibroblast cells was observed when lunasin was added exogenously at nanomolar concentrations. In addition, topical application of lunasin inhibited skin tumorigenesis in female SENCAR mice. Lunasin peptide has also been shown to induce apoptosis in E1A-transfected C3H10T1/2 cells (Galvez et al., 2001) and suppress foci formation in E1A-transfected mouse fibroblast NIH 3T3 cells (Lam, et al., in press). E1A is a viral onco-protein that inactivates the Rb (retinoblastoma) tumor suppressor (Nevins, 1992). Furthermore, when C3H10T1/2 and MCF-7 human breast cancer cells were treated with lunasin in the presence of the histone deacetylase inhibitor, sodium butyrate, a 10- to 95-fold reduction in acetylation of core histones H3 and H4 was observed (Galvez et al., 2001). The genome-wide reduction in core histone acetylation suggests an epigenetic mechanism of action for lunasin that can influence gene expression fundamental to carcinogenesis.
Prostate cancer is the most common non-dermatological carcinoma in the United States with an estimated 220,900 new cases and 28,900 deaths in 2003 (ACS, 2003). This type of cancer is the second leading cause of death among American men (www.cancer.org). Effects of anticancer agents on gene expression profiles of prostate cell lines using cDNA microarray analysis have been reported (Kudoh et al., 2000; Li et al., 2003; Zembutsu et al., 2003).